Computational Fluid Dynamics (CFD) allows researchers and practitioners to analyze cyclist aerodynamics and identify areas for improvement. Despite the numerous CFD simulations of cyclist aerodynamics in the scientific literature, the extent to which user choices in the large number of computational parameters affect the simulation results remains largely unexplored. This paper aims to establish a set of best practice guidelines for CFD simulations of an isolated cyclist in time trial position through a systematic and comprehensive sensitivity analysis. It includes the computational grid in terms of surface, near-wall, and far-field volume grids and the turbulence modeling. The study reveals a high sensitivity of the computed drag area to the surface grid resolution and y+ value, while the impact of the growth rate and the grid resolution in the wake is relatively smaller. The results emphasize the importance of complete reporting of grid characteristics and the need for grid-sensitivity analyses, and provide prioritization of the key parameters for such analyses. Satisfactory agreement with wind tunnel measurements is achieved using Scale-adaptive simulations (SAS) and steady RANS with the Transition SST (T-SST) or SST k-ω turbulence model for closure. This work intends to contribute to accurate and reliable CFD simulations of cycling aerodynamics.
This paper discusses a procedure for the two-way run time external coupling between Building Energy Simulation (BES) and building envelope Heat, Air and Moisture (HAM) programs for enhanced wholebuilding simulation. The coupling procedure presented here involves a description of the relevant physical phenomena at the interface between the programs, domain overlaps, coupling variables, coupling strategy and types of boundary condition. The procedure is applied using the programs ESP-r and HAMFEM, where the implementation and verification issues are discussed. This work concludes that the coupling between BES and HAM programs is feasible, and it can potentially enhance the accuracy in whole-building simulation.
An overview of research on rainwater runoff from building facades is presented. Observations, on-site measurements, laboratory measurements and modelling efforts are discussed. While observations are many, on-site experiments and modelling efforts are few and have been almost exclusively made at plain facades without details. To the knowledge of the authors, current hygrothermal models do not yet contain runoff models. Implementation of runoff models is an important requirement for the upcoming 2D and 3D generations of HAM models.<br/><br/>\nUn survol de résultats de recherche sur l'écoulement de l'eau de pluie sur les façades de bâtiment est présenté.\nNous discutons des travaux d'observation, de mesure en laboratoire, et par simulation sur ordinateur. Alors\nque les observations in situ sont nombreuses, il y a peu de travaux expérimentaux ou de modélisation, et ce\nseulement pour des façades tout à fait planes. Aussi, à notre connaissance, les outils actuels de modélisation\nhygrothermique ne tiennent pas compte de l’écoulement de l'eau de pluie. Le développement et\nl'implémentation de modèles d'écoulement de l'eau de pluie est une spécification cruciale pour les prochaines\ngénérations de modèles hygrothermiques, en deux ou trois dimensions.
Abstract: Knowledge of microscale wind conditions is important for maneuvering and mooring of ships and for optimizing the harbor design. The aim of this study is to translate the macroscale wind conditions measured at a near shore reference station to the local (microscale) wind conditions in the harbor docks. In the first part of the project, an extensive experimental campaign has been performed, which consisted of wind velocity measurements with 2D and 3D ultrasonic anemometers during a period of 6 months. These point measurements confirm the unique relation between the macroscale and microscale wind conditions during periods of strong winds. As the measurements only provide information at a number of discrete positions, the second part of the study consists of numerical simulations with Computational Fluid Dynamics (CFD) to map the wind environmental conditions over the entire study area. The measurements and simulations both show very large gradients in mean wind speed over the harbor area, with differences up to 100%. The numerical simulations are currently in progress and will be validated by comparison with the on-site measurements.
CFD simulations of the wind speed conditions in passages between generic parallel building configurations are performed. CFD validation is conducted based on published wind tunnel data. The computational results agree well with the experimental data when an appropriate grid resolution is employed. The required grid resolution across the passage width appears to be a function of the passage width and the building influence scale. A grid resolution guideline is provided. Finally, the simulations and the measurement data are used to identify three different types of passage flow as a function of the dimensionless ratio of passage width to building influence scale.
The accuracy of CFD simulations of vertical axis wind turbines (VAWTs) is known to be significantly associated with the computational parameters, such as azimuthal increment, domain size and number of turbine revolutions before reaching a statistically steady state condition (convergence). A detailed review of the literature, however, indicates that there is a lack of extensive parametric studies investigating the impact of the computational parameters. The current study, therefore, intends to systematically investigate the impact of these parameters, on the simulation results to guide the execution of accurate CFD simulations of VAWTs at different tip speed ratios (λ) and solidities (σ). The evaluation is based on 110 CFD simulations validated with wind-tunnel measurements for two VAWTs. Instantaneous moment coefficient, Cm, and power coefficient, CP, are studied for each case using unsteady Reynolds-averaged Navier-Stokes (URANS) simulations with the 4-equation transition SST turbulence model. The results show that the azimuthal increment dθ is largely dependent on tip speed ratio. For moderate to high λ, the minimum requirement for dθ is 0.5° while this decreases to 0.1° at low to moderate λ. The need for finer time steps is associated to the flow complexities related to dynamic stall on turbine blades and blade-wake interactions at low λ. In addition, the minimum distance from the turbine center to the domain inlet and outlet is 15 and 10 times the turbine diameter, respectively. It is also shown that 20–30 turbine revolutions are required to ensure statistically converged solutions. The current findings can serve as guidelines towards accurate and reliable CFD simulations of VAWTs at different tip speed ratios and solidities.
This paper presents wind tunnel measurements of pedestrian wind conditions in passages between various configurations of two long narrow perpendicular buildings in open country exposure. The investigated parameters include passage width, building height and wind direction. The measurements were made along the passage centerline. The aim of the paper is to provide more insight in the pedestrian wind conditions in these basic building configurations, to address some contradictory statements reported in the literature and to provide experimental data for CFD validation. The results show that, for the cases investigated, the amplification factors in diverging passages are generally larger than in converging passages. It is also shown that the maximum amplification factors increase monotonically with decreasing passage width, contrary to some general building design guidelines proposed in the past for all building configurations.
This paper explores the use of computational fluid dynamics (CFD) in the design of cycling skinsuits with varying surface roughness. Traditional skinsuit design involves a complex and time-consuming process by wind tunnel experiments. CFD could potentially offer an alternative for predicting the performance and designing rider-specific skinsuits, though accurately modelling fabric surface roughness is challenging. The study characterizes skinsuit fabrics based on an equivalent sand-grain roughness height (k<sub>S</sub>) value derived from drag reduction measurements on cylinders covered with specific fabrics. Three skinsuits, created from these fabrics, are assessed on a full-scale cyclist mannequin. For two of the three suits, the calculated drag area is within 0.6 % of the wind tunnel (WT) results. In the case of the third suit, the deviation with the WT drag area is 1.6 %. The CFD simulations reveal valuable insights, such as the impact of including variable k<sub>S</sub> values on the location of flow separation, the local distribution of skin friction and pressure drag, and their effects on the near flow field. The agreement between WT and CFD results suggests the potential of CFD for designing aerodynamically optimized skinsuits for individual riders, while further research is recommended to refine and validate this approach.
